Field of the Invention
The invention relates to a circuit configuration for intermediate frequency demodulation for a video signal processing device, including a first filter with a bandpass characteristic, to which an input signal at an intermediate frequency can be delivered and by which a video signal in an IF position is generated, a second filter with a bandpass characteristic, to which the input signal can be delivered and by which a video carrier signal is generated, and a demodulator, by which the video signal is converted in the IF position into a base band.
The invention also relates to a video signal processing device that includes such a circuit configuration.
In video signal processing devices, such as television sets, the frequency band of a selected transmitter is chosen through the use of a tuner, and from that band the frequency range of the selected transmitter is in turn converted into a constant intermediate frequency (IF). The video signals, transmitted by the asymmetric sideband transmission, are modulated into a video carrier. The sound carrier is located at the periphery of the picture signal spectrum. In order to ensure the least possible influence on the video signal and the sound carrier upon the conversion to the base band, the video signal carrier, as described in German Published, Non-Prosecuted Application DE 37 18 103 A1, corresponding to UK Application GB 2 191 367 A, is recovered in a further branch through the use of a suitably constructed bandpass filter. This bandpass filter is then used in the video signal branch to convert the video signal from the IF position into the base band. Since the recovered video carrier must be in phase with the video signal in the IF position as much as possible, the various filters and optionally provided control amplifiers must meet more stringent demands in terms of the signal delay time.